Musical instrument



F. A. #msx-STONE MUSICAL INSTRUMENT 3 sheets-sheet 2 Filed Sept. 6, 1938 y EA. AERESTONE 29%@9253 MUSICAL "LNSTRUMENT lFiled Sept. 6, 1938 3 Sheets-Sheet 5 Patented July 22, 1941 MUSICAL INSTRUMENT Floyd Firestone, Ann Arbor, Mich., assignor, by mesne assignments, to Hammond Instrument Company, Chicago, Ill., a corporation of Dela- Ware Application September 6, 1938, Serial N o. 228,477

16 Claims.

This invention relates to electrical musical instruments of the same general class as the invention disclosed and broadly claimed in United States Patent No. 1,953,753, granted to me on April 3, 1934.

In my aforestated prior patent use is made of a multiplicity of capacitance reactance assemblies for producing alternating voltages at different tone frequencies. Said patent teaches how such assemblies can be used for the production of alternating voltages\at harmonically related tone frequencies and substantially sinusoidal waveform, adapted selectively to be irnpressed upon the grid circuit of an electron tube amplier and at controlled relative intensities to produce any desired complex waveiorm'in the output circuit of said amplifier. Twelve similar reactances properly formed and driven in ratios of 1 to 1172 will produce alternating voltages .at-frequencies conforming to all fundamental tones of an even tempered musical scale and a predetermined number of harmonics of said fundamental tones.

In the embodiment of my invention now sought to be protected by Letters Patent, twelve identical capacitance reactances are employed, the forms, shapes and relationship of parts of each thereof being such as to insure production of larger and consequently more useful voltages than Was possible heretofore.

An important feature of the invention is to provide a capacitance reactance embodying relatively rotatable undulatory instrumentalities in scanning relation to each other, the forms of which, aside from producing .larger and more useful voltages Will insure continuous production of substantially sinusoidal waveforms.

Another object is to provide an arrangement of identical capacitance reactances constituting a simple and exceedingly compact and light weight organization of voltage generators adapted readily to be accommodated in a small easily portable console.

A further important object of the invention` is to providey means for shielding adjacent capacitance zones to prevent modulation of a tone by stray electrostatic uX induced at any Zone not being drawn upon at the instant desired voltages are lbeing conducted from others of the zones for the production of said tone.

Another object is to provide capacity reactances having rotatable instrumentalities serving as an inertia mass to counteract an otherwise objectionable effect of fluctuants occurring at the driving source or in the power transmission between said source and said scanning instrumentalities, thus to hold sensibly constant the necessary speeds of said instrumentalities and prevent changes in the pitch relation of the produced tones.

In the accompanying drawings:

Figure 1 is a schematic plan view of my improved system of capacitance reactances; v

Figure 2 is a view in end elevation of the system shown in Figure 1; l

Figure 3 is a Vertical section through one'of the multiple capacitance reactances shown in Figure 1;

Figure 4 is a schematic view in plan of a primary electrode and associated undulatory scanning instrumentality;

Figure 5 is a view in perspective of a primary electrode;

Figure 6 is a view in elevation of a scanning instrumentality common to a plurality of primary and secondary electrodes;

Figure 7 is a view in elevation of an assembly of primary and secondary electrodes;

Figure 8 is a schematic illustration of a slightly modified form of the invention in which two electrodes, each of undulatory form are in scanning relation to each other, and- Figure 9 illustrates a further modification of the invention.

The system of continuously varying capacitance reactances shown VinFigure 1 of the accompanying drawings is broadly similar to the continuously Varying reactance groups or assemblies 40 shown at Figure 3 in my aforestated prior patent. In one form ofthe invention herein disclosed, each capacitance reactance includes a scanning instrumentality, preferably, but not necessarily in the form of a rotatable metallic disc 20, connected to earth and provided with suitably spaced apart concentric circles'of scanning areas 2|, the distance between the adjacent areas in any circle being an integral multiple of any individual capacity area of an associated primary electrode, the form of which will be described presently. Eight circles of scanning areas are provided for each of said discs. The

inner circle comprises 2 scanning areas, the nextV circle 4 such areas, the next 8 such areas; the next 16 such areas and so on to the outer circle of the series which has 256 of such areas. Thus, the grouping of the respective scanning areas is in the mathematical order of frequencies in octave relation. Assuming disc 20 in Figure 6 to represent the disc C at the extreme left of Figure l of the drawings, it is apparent that it is a part of a multiple capacitance rreact'ance adapted to produce alternating potentials at the tone frequencies of all C notes of a musical scale. Similarly, the next disc above disc C is a part of a multiple reactance for producing alternating potentials at tone frequencies of all Cl notes and so on to the last of the twelve discs which forms part of a reactance for producing potentials at frequencies for all the Bf notes. If as proposed herein, the ratio between any rotatable reactance and any other reactance above it is and if the numbers of scanning areas in the eight circles of the disc progress geometrically exactly in the same ratio, the tone frequencies of the generated potentials will be in equal temperament. While I show conventional belts and pulleys for transmitting these necessary incommensurate speeds to the respective discs in Figure 1, it is understood that any well known means can be substituted therefor without departing from the spirit of my invention. These speeds can readily be approximated by the system of gears disclosed in the patent to E. G. Thomas, No. 1,156,329, dated Oct. 15, 1915.

Said discs 20 may each be approximately 51/2 or 6 inches in diameter and about fs of an inch in peripheral width. In Figure 1 the twelve discs 20 are coaxially related to each other and each is iixed to its own driven shaft 22 having a pulley 23. At 24 is a drive shaft having pulleys 25, there being one thereof for each of the driven pulleys 23, the former connected to the latter by belts 26. The ratios of the diameters of adjacent pulleys 25 are 1 to l2/ 24 The drive shaft 22 is belted or otherwise geared in some well known manner to a synchronous or other suitable constant speed motor 21.

Disposed at one side of each of the discs 20 is an electrode assembly 28. A detailed description of one of these assemblies will sufce for the entire series as they are all identical in every respect. Upon reference to Figures 3 and 7 of the drawings, 2|| represents a mounting or support of non-conductive material. Extending from one side of said mounting are primary waveform electrodes 2S and secondary electrodes 30. Upon reference to Figure 7 it is noted that there are four groups of primary and secondary electrodes 29 and 30, there being one secondary for each pair of correlated primary electrodes in each of said groups. In this manner alternating voltages at different tone frequencies can be conducted to a work circuit from a common secondary electrode. Each secondary electrode comprises an arcuate continuous, smooth surfaced, brass plate, concentrically spaced apart from similar brass plates 3| to which the primary electrodes are iirmly cemented in flatwise positions as shown in Figure 7 and insulated therefrom by thin strips of mica 332 or other Well known insulating material.

In Figures 4 and 5 a form of primary electrode is shown for the continuous production of a substantially sinusoidal waveform in co-action with a correlated circle of scanning areas 2| on disc 2D. In each of these figures, the primary electrode consists of a thin at plate of conducting material having lateral, eiTective capacity areas 3| I, equi-distantly spaced apart from each other.

The scanning areas of disc 20 in Figure 4 are` spaced from each other a distance about the center of shaft 22 equal to the angular distance between teeth of the coacting electrode 29.

I nnd in actual practice that to produce large voltages for all tone frequencies the number of effective capacity areas per primary electrode should progressively increase in the direction of the higher frequencies. This is so because of the gradual diminishing surface proportions of the scanning areas in the direction of the outer high frequency circle in Figure 6. 'Ihe low frequency primary electrodes, however, have each but a single capacity area. The electrodes for thenext two higher frequencies each have two such areas.

In Figure 3, the disc 20 is operatively associated with an' electrode assembly so that during continuous rotation of said disc at its assigned speed, capacitance changes will occur between the respective primary and secondary electrodes with resulting production of alternating voltages in octave relation to each other, any one or more of which can be conducted to a work circuit to control a loud speaker. A network suitable for selective use of the voltages at different relative intensities is shown in my aforestated prior patent. In said Figure 3 and as will also be appreciated on reference to Figure 7, it is noted that the outer two brass plates 3| of each group of primary and secondary electrodes serve to shield this capacitance zone of the device from the effects of shifting electrostatic flux generated at zones provided by others of said groups. In this manner, a tone is sounded without being modulated by otherwise disturbing static effects occurring at electrodes from which no alternating voltage is being drawn at a particular instant.

Upon referring again to Figures 3, 6 and '7 and particularly on reference to Figure 3, it is noted that all primary and secondary electrodes of each of the aforestated groups of electrodes are at a xed radial distance apart from each other and are also uniformly spaced radially from scanning portions in an associated circle of the disc. By reason thereof and due also to the manner of supporting the disc for rotary motion, the spacing of these parts is held effectively constant and unwanted tremolo effects avoided when sounding any tone.

From the construction herein set forth, it follows that when disc 20 is rotated, the primary electrodes will be periodically exposed to `the secondary electrodes, the electrostatic 'capacity between them being always greater when a space between adjacent scanning portions of the disc is opposite them. The disc is grounded at 200. The brass plates 3| are each grounded, as shown at Figure 3. Connection with a source of charging potential is made through input leads 300. All of the secondary electrodes connect with the input of an electron tube amplifying system 400, in the output circuit of which is an electrical sound producer 500.

I stress the feature which consists in using grounded shields 3| between which is disposed a secondary electrode 30 serving two primary electrodes 29, thereby simplifying the construe tion and reducing capacity to ground by one half while yielding increasing voltage.

While I show discs 20, each constituting a scanning vinstrumentality common to a plurality of waveforms and adapted to originate voltages ref spectively `conforming to notes in octave relation,

`strength is generated at each electrode.

it is vunderstood that this arrangement obviously ,can be modified-without departing from the spirit of the invention.` Thatis to say, the discs 20 can beformed so that each thereof will generate fundamental tone frequencies in octave relation and .all frequencies that are harmonics of said funda- -mental :tone frequencies Such arrangement is provided for inmyaforestated prior Patent No.

- InFigure 8 va disc 1&0 ris shown, the same being l #substantially .like disc in the rst embodiment Y of myy invention, andhas concentric'circles of capacity areas 125. Said "disc is insulated from a drlvenshaft 150 on which it is fixedly mounted and is connected by conductor 115 to the input circuit 180 of an electrontubeamplifier. v disc thus serves as asecondaryr electrode in co- 'a'ction with .an insulated, primary electrode 800, thelatter connected to a direct current supply `The source 825. `The primary electrode isthe same as any electrode 29 in said rst embodiment of my invention." In this yform of my invention there, of course,wil1 be one primary electrode for each circle of combinedscanning and capacity areas on the disc 100.

Inl the form ofmy invention shown in Figure 3,-the disc is of Lany material as it merely is employed as a scanning instrumentality. .In fthe form shown in Figure 8, however, the disc functions in the dual capacity of an electrode means' .and scanning instrumentality Iand therefore is ,formed entirely of metal.

The `sets' of `circles of scannersmay be milled in a circular piece of metal, fthey normal thickness of which is equal to thek rim width. The'individual equi-distantly i electrode either in Figure 3 or Figure 8, are each y.substantially `of the same shape and :surface dif mensions as vany individual scanning area or tooth ofk an associated circle of scanning forms, and asy they 4are spaced apant the same as said teeth or areas: of said Iassociated circle, it follows that the angular relation of the latter to rthe former is always the same at any moment during relative rotation of these parts. I nd in practice that parts of the relative shapes rherein shown produce periodic .capacitance changesxand alternating voltage of substantially sinusoidal waveform. rI find also that by increasing fthe number of waveform teelth or areas on'the primary electrodes in the direction of the higher frequencies, voltage of substantial In other words,` the dimensions are precalculated so that the combined capacity areas of any electrode is almost the same as the combined area or areas of any scanningy form or forms coacting therewith at any-instant, therespective parts be- -ing such that the space between adjacent scanning areas is equal to an integral multiple of the -v 'Wavelength of Ithe effective capacity area of a coacting electrode. The arrangement of scantirely eifective'when coacting with a likenum- 4ber -of scanning forms in the associated circles on disc 20. They may, however, extend as far as desired about the axis of rotation of sai-d disc if larger voltage is desired.

I further find in practice that by covering the Bakelite support 2li, Figure 3 with black conducting paint, except directly around the insulators 332, the latter being entirely concealed behind the primary electrodes 29, extraneous noises, due to charges collecting on said insulators are reduced.

'I'he voltage input leads 380 shown in Figure 3 will o-f course connect to a polarizing source in a network which may be as shown in Figure 4 of my prior patent, the same including playing `keys, each having multiple contacts connected in the network and with the voltage generators so that when a key corresponding .to a selected note is depressed, preselected generators will be drawn upon and the generated voltages impressed upon the input circuit of the amplifier 400. `No claim is made herein for any particular meansl enabling the various voltages itc be utilized for the production of preselected tone timbres. Reference herein to my prior patent will be sufficient to enable persons skilled in the art to which the invention relates to carry same into practice as intended. It will suiiice to say that alternating voltage generators characterizedv as herein set forth can be used in any well known network having keying means and employing timbre determining stops.

,While I show and have described rectangular 'teeth on a rotary Vmember the space between which is equal to the length of any coacting similar tooth of an associated primary electrode, early experiments disclosed that at the higher frequencies, van inductor having teeth, the space between them being 21K.; times the widlth of the tooth itself, gave no harmonic as large as 1%, the reason being that the clearance between the electrode teeth and the teeth of the rotary member is an appreciable fraction of the distance between adjacent teeth on the inductor and the fringing of the linesV of force around the teeth is such yas to smooth out abrupt changes of capacity, yielding an` approximately pure wave.

In Figure 9 of the drawings is disclosed a further modifled form of combined scanning instrumentality and electrode means, the same comprising a magnesium disc having concentric undulating rings 50, each forming one wall of a groove 60 cut in one side of the disc. Coacting with each set of undulations is an electrode f 10, also of undulatory form. The electrode 10 may be connected to a polarizing source, and by means of a slip ring (not shown), the disc can be connected in the input circuit of an electron tube amplifier in the manner shown in Figure 8. Discs of the form shown in Figure 9 can be used advantageously for generating voltf ages of higher frequencies and can be used in frequencies.

combination with a disc of the kind shown in Figure 3, formed to generate voltages of lower The width of the groove at each of the rings of undulations 50 .is suiiicient to accommodate the electrode 10 and enable it to be disposed in concentric inductive relation to vsaid undulations.

What I claim aspmy invention is:

1. In an electrical musical instrument, a continuously variable condenser having a combined scanning instrumentality, an electrode providing a continuous succession of solid scanning and capacity areas of one piece of conductive material; and a coacting electrode providing a similar succession of solid capacity areas, all of which are in a plane parallel to the path of movement of the scanning and capacity areas and are formed of one piece of conductive material.

2. In an electrical musical instrument, a continuously varying condenser comprising respective devices including electrodes forming one device and scanning means forming another device, said devices coacting to cause simultaneous capacitance changes at the electrodes at respective rates conforming to the vibrational frequencies of different musical tones; means for moving said devices relatively to cause the aforestated capacitance changes; means for guarding each electrode from the effects of shifting flux fields generated at any other electrode; and means enabling selective conduction to a work circuit of one or more voltages produced in response to said capacitance changes.

3. In an electrical musical instrument, a continuously varying condenser comprising an electrode of undulating configuration; means for polarizing said electrode; and means coacting with said electrode to scan same at a rate to vary the capacitance of the generator according to a given tone frequency, the undulating configuration of the electrode presenting at one edge of the electrode capacity areas in side by side relation, the scanning means having effective straight sided scanning portions spaced apart from each other a distance equal to the Wavelength of any capacity area of said electrode.

4. In an electrical musical instrument, a continuously varying condenser comprising a rtatable disc having concentric circles of scanning areas different in number from each other: a plurality of electrostatic shields; primary electrodes mounted atvvise against the respective shields; and electrically insulated therefrom; a secondary electrode common to said primary electrodes; and said shields being of lengths relative to their electrodes to protect one electrode from the eects of shifting electrostatic flux fields generated at any other electrode; and means for driving the disc at constant angular velocity to effect capacitance changes at the electrodes and simultaneous production of alternating voltages at different tone frequencies.

5. In an electrical musical instrument, a continuously varying condenser organization, a rotatable metallic member constituting a combined scanning instrumentality and secondary electrode adapted to impress alternating voltages at different tone frequencies upon the input circuit of an electron tube amplifier through a single electrical conductor, said member having a plurality of concentrically related sets of scanning forms; and a primary electrode foreachsetofsaid scanning forms inductively related thereto and adapted to be sequentially scanned thereby during rotation of the member relative thereto and thereby produce alternating voltage of predetermined tone frequency.

6. In an electrical musical instrument, relatively rotatable capacitatively related electrodes, one of which comprises a single piece of sheet metal formed with integrally connected and equidistantly spaced apart capacity areas providing a Waveform pattern, the other electrode comprising a metallic member having a set of capacity areas, said areas of said set spaced apart from each other a distance equal to an integral multiple of any one of the rst named capacity areas and means for moving the electrodes relatively to cause a scanning of the first named areas by said second named areas at a rate conforming to the vibrational frequency of a predetermined musical tone.

7. In an electrical musical instrument, a continuously varying condenser including a plurality of electrodes insulated from each other; `a rotatable member having a plurality of concentrically related sets of scanning forms related to the respective electrodes simultaneously to scan same, each set of forms comprising a number of integral parts of said member adapted periodically to scan an associated electrode and cause capacitance changes at said electrode conforming to the vibrational periodicity of a predetermined musical tone; and means for mounting the electrodes to dispose same in operative coaction with the respective sets of scanning forms and providing electrostatic shielding to guard an electrode from the effects of shifting flux fields occurring at and in the proximity of any other electrode during operation of the generator.

8. An electrical musical instrument, a continuously varying condenser comprising a stator assembly having spaced apart primary electrodes; a mounting of insulating material for said electrodes; grounded metallic shields carried by the mounting or guarding an electrode from the effects of flux disturbances occurring at any other electrode during operation of the condenser; secondary grounded electrodes supported by said mounting and associated capacitatively with coacting primary electrodes; electrical conductors for conducting voltages from the secondary electrodes; and means by which the primary electrodes are periodically exposed to associated secondary electrodes at rates simultaneously to electrostatically originate alternating voltages at different tone frequencies.

9. A combined scanning instrumentality and electrode for variable condensers for producing alternating voltage of the frequency of a predetermined musical tone comprising a rotatable metallic disc grooved at one side in an axial direction and disposed concentric to the axis of rotation of the disc and having an undulating Wall, said groove adapted to accommodate an electrode and enable same to be inductively related to said undulating wall.

l0. In an electrical musical instrument an alternating voltage originating system comprising relatively movable organizations, one of which comprises concentric circles of spaced apart capacity areas, the other organization having means capacitatively related to said capacity areas, electrostatically to originate alternating voltages at different tone frequencies; means for polarizing one of said organizations; means enabling said alternating voltages to be impressed upon a Work circuit, the capacity areas being shaped to cause each of the voltages to follow a substantially sinusoidal Waveform; and means for guarding the capacity areas from the effects of shifting electrostatic flux originating any place in the system during relative motion of said organizations.

1l. In an electrical musical instrument, a plurality of variable condensers having electrodes respectively provided with different numbers of capacity areas; means common to all of said `condensers for simultaneously and continuously scanning the capacity areas of said electrodes periodically at relative rates to electrostatically develop alternating voltages at different tone frequencies; and means for guarding each condenser from the effects of stray electrostatic flux originating at any other condenser.

l2. In an electrical musical instrument, a continuously varying condenser comprising an electrode consisting of a disc Wholly of conductive material; means for continuously driving said disc at an invariable velocity, said disc having a concentric circle of annularly spaced apart capacity areas; an electrode disposed relative to the disc electrode to be periodically scanned by capacity areas thereof; and a source of D. C. potential ior oppositely charging said electrodes to thereby electrostatically originate alternating voltage of predetermined tone frequency during continuous relative rotation between them.

13. In an electrical musical instrument, concentrically related pairs of capacitatively related primary and secondary electrodes; a grounded metallic disc having at least one or more capacity areas for each pair of primary and secondary electrodes and disposed relative to said electrodes periodically to expose one thereof to the other during continuous rotation of said disc; a source of D. C. potential for oppositely charging the primary electrodes of each pair of said electrodes; and means for continuously driving said disc periodically to effect exposure ci the secondary electrodes to the primary electrodes as aforestated.

14. In an electrical musical instrument, a conm tinuously varying condenser organization consisting of a secondary electrode having concentric circles of annularly spaced apart capacity areas, the number of such areas in any circle being different from the number in any other circle; a primary electrode for each circle of the aforementioned capacity areas and provided with one or more capacity areas, each having surface dimensions substantially the same as the surface dimensions of any individual capacity area in said circle; a source of D. C. potential for charging said primary and secondary electrodes; means mounting said electrodes to capacitatively relate their capacity areas to each other and enable continuous relative motion between said electrodes; and means for causing said continuous relative motion between said electrodes.

l5. In mechanism of the class described, a continuously varying condenser organization including concentrically related pairs oi primary and secondary electrodes, the primary and secondary electrodes oi each pair of said electrodes being capacitatively related to each other and adapted to be oppositely charged from a source oi D. C. potential; an electrostatic shield associated with the primary electrode of each pair; and a rotatable member driven at an assigned speed and having concentric circles of scanning areas, there being one such circle of scanning areas for each pair of electrodes and the number of said areas being predetermined and coacting with said electrodes periodically to expose one of said electrodes to the other and thereby electrostatically originate a Waveform of alternating voltage of predetermined tone frequency; and means at each pair of primary and secondary electrodes providing a constant leak to ground for stray electrostatic charges generated during the aforementioned periodic exposure of the electrodes to each other.

16. In` mechanism oi the class described, a continuously varying condenser organization including concentricaliy related pairs of primary and secondary electrodes, the primary and secondary electrodes of each pair of said electrodes being capacitatively related to each other and adapted to be oppositely charged from a source of D. C- potential; an electrostatic shield associated with the primary electrode of each pair; and a rotatable metal disc constantly connected to ground and driven at an assigned, invariable speed and having concentric circles of scanning areas, there being one such circle of scanning areas for each pair of electrodes and the number of said areas being predetermined and coasting with said electrodes periodically to expose one electrode to another and thereby electrostatically originate a Waveform of alternating voltage of predetermined tone frequency; and means at each pair of electrodes providing a constant leak to ground for stray electrostatic charges generated during the aforementioned periodic exposure of the electrodes to each other.

FLOYD A. FIRESTONE. 

